Fix #571: Footer broken on RTD site
Remove stuff that's not needed for the theme
Update copyright

The copyright in the build configuration file shows in the default
footer.
Hide default footer in docs by hiding default copyright

The default footer only consists of the copyright statement, so we
can get rid of the footer by not showing the copyright.

Instead we show a custom footer thanks to @umcsdon.
Fix #501 Warn user about losing new talk info

When the user switches from one talk to another, exits the talk editor,
or creates a new talk when the currently selected talk has unsaved
changes, a window comes up warning the user that there are unsaved
changes. The options are "Save Changes", "Discard Changes", and
"Continue Editing".

Fix #501
Close #605
Fix #476 Auto language changing function finished.

Fixes 476.
If the user does not have the freeseer.conf file, the function will detect the system location for default language.
If there is a config file, the language setting in that file will have higher priority.
For Chinese, If the location is not zh_CN, Traditional Chinese will be used.
If there is no translation for the system location, English will be used.
Solve the python standard formation problem in code.
Delete the redundant backslash to fit the format requirement.
Delete the trailing space to fit the format.
Pass config argument to FreeseerApp to solve the duplicated code problem when doing the auto language changing.
Fix the format problem of missing whitespace.
Modify the code according to the code review. This version is not yet functional because of some bug.